P13.04: Does genomic microarray add prognostic information in case of the second trimester small‐for‐gestational age, but structurally normal fetus?

In case of small for gestational age fetal growth, the chance of fetal chromosomal anomalies is increased up to 19%. This chance is influenced by the gestational age at onset of growth impairment and the concomitant presence of structural ultrasound anomalies. Genomic array is increasingly used to detect fetal chromosomal abnormalities. This study evaluates the value of prenatal SNP array testing in second trimester small for gestational age fetuses without structural ultrasound anomalies. 59 Pregnancies with second trimester (18-24 weeks of gestation) small fetal growth (abdominal circumference p < 5) without signs of structural anomalies on ultrasound between July 1st 2012 and November 25th 2013 at the Erasmus MC prenatal clinic were selected for this analysis. Every patient was offered invasive rapid aneuploidy detection (RAD) by QF-PCR and SNP array testing with a resolution of 0.15Mb. Follow-up until one month after birth was collected. 29 of these 59 patients opted for invasive testing. In these cases the growth impairment was more severe (mean AC percentile 1.33 versus 2.35; p0.02) and it was more often accompanied by nonstructural anomalies (such as echogenic bowel and oligohydramnios; 48% versus 30%) compared to the patients that declined invasive testing. Prenatal SNP array testing (n = 28) showed no abnormalities (RAD detected one case of trisomy 21). After birth, further genetic testing was indicated in 4 fetuses and infants. Of those not subjected to prenatal testing (n = 30), 3 showed signs of a genetic anomaly after birth. One infant had trisomy 21. Postnatal SNP array testing in the other 2 cases did not show abnormal results related to the observed phenotype. These preliminary results suggest that SNP microarray testing might be of limited value in pregnancies affected by isolated second trimester fetal growth impairment.The use of NIPT may be considered for this indication. Further research on larger cohorts is required to investigate this hypothesis.